Test Center: SANs tuned for virtualization pack nice surprises

Virtualization is moving further into the datacenter all the time, with even critical large-scale applications like Exchange and databases now being virtualized. Whether you're using virtualization to make large applications more manageable or to consolidate many small applications, a server with lots of RAM, lots of processor cores, and lots of I/O is a good thing. And so is a SAN packed with features that ease the management of storage for virtual machines.

[Editor's note: This article has been revised to remove comparative statements regarding performance of the SANs. Performance was not tested.]

From a storage viewpoint, each virtual machine uses a file to simulate a physical hard disk. This file, a VMDK (Virtual Machine Disk Format) under VMware or VHD (Virtual Hard Disk) under Microsoft, can be located on a server's internal drive or on a SAN. There are several advantages to putting the file on a SAN: The file can be duplicated using the storage's snapshot function, the file can be moved easily from one hardware server to another for scalability or fault tolerance, and the storage itself can be more easily made fault tolerant.

[ See the Test Center reviews: VMware vSphere 4: The once and future virtualization king | Microsoft's Hyper-V R2 is hot on VMware's heels. ]

I tested five midrange SAN systems that deliver the goods for virtual environments: the Compellent Storage Center 4.0, the Dell EqualLogic PS4000, the HP StorageWorks 2000sa G2 Modular Smart Array, the Pillar Axiom 600 from Pillar Data Systems, and a build-it-yourself pairing of the Promise vTrak E610f hardware and DataCore's SANmelody 3.0 storage software. This review focuses on these systems' virtualization-friendly features. For a close look at the full range of their capabilities, see Network World's companion review.

The prices (as tested) of these systems range widely, from less than $10,000 for the Promise Technologies and DataCore combination to $130,000 for the Pillar Data system. All the manufacturers have models ranging from inexpensive starters to very high-performance datacenter-ready systems. As you can tell from the range in price, the models I tested don't necessarily compete with each other.

My five SANs also differed in their connectivity options, a factor that made an apples-to-apples comparison of I/O performance infeasible. For example, the HP is Fibre Channel only, the Dell is Ethernet (iSCSI) only, and the other three systems support both Fibre Channel and Ethernet. My testing therefore focused on features and functionality rather than IOps, which can vary widely even across SAN models from the same manufacturer.

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